Androgens are indispensable for normal spermatogenesis; however, the mechanism by which androgens exert their effect on this complex process is poorly understood. Androgens act on their target cells by binding to and activating the androgen receptor (AR) present in Sertoli cells, peritubular cells, and Leydig cells but not in germ cells. It is assumed that androgens' actions on spermatogenesis are mediated by paracrine signals resulting from changes in gene expression in Sertoli and peritubular cells. In spite of an intensive research effort for several decades, traditional methods have failed to pinpoint key androgen-regulated genes whose activation is critical for spermatogenesis. We have studied a transgenic mouse model that overexpresses androgen-binding protein (ABP), a secretory product of Sertoli cells. These transgenic animals develop a progressive impairment of spermatogenesis and become gradually infertile. The results of our morphological, immunocytochemical, and flow cytometric analyses of the testes indicate that the most likely cause of this impairment is the reduction in the concentration of bioavailable androgens in the peritubular compartment and the seminiferous tubules. DNA microarray technology offers a novel and powerful means to analyze gene expression in a comprehensive, yet efficient, way. The Specific Aim of this pilot project is to test the hypothesis that the chronic reduction of bioavailable androgens within the seminiferous tubules of the ABP-transgenic mice is manifested in ordered changes in gene expression detectable by DNA microarray analysis. Murine genome oligonucleotide arrays will be probed by cRNAs prepared from testes of wild type and transgenic mice of 30 days of age. As additional controls, a set of the transgenic animals will be treated with human chorionic gonadotropin. This treatment is known to increase intratesticular androgen concentration and should reverse the changes caused specifically by androgen depletion. Results will be analyzed in terms of expression levels, expression profiles (dendrograms) and functional relationships. Cellular localization of altered gene expression will be determined by in situ hybridization and immunocytochemistry. This strategy is likely to provide, for the first time, a comprehensive view of androgen-dependent genes in the mammalian testis, offering a rich source of information for further studies, new clues for understanding and treating certain cases of human male infertility, and new potential molecular targets for male contraception.